Yes, VOLT is a Scrabble word!

Letter values in Scrabble US: V 4, O 1, L 1, T 1.

Is it a valid word?

VOLT is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a unit of potential equal to the potential difference between two points on a conductor carrying a current of 1 ampere when the power dissipated between the two points is 1 watt; equivalent to the potential difference across a resistance of 1 ohm when 1 ampere of current flows through it

Also: v.